A. Field of Invention
This invention relates to the field of intraluminal devices and particularly to intraluminal grafts useful as an inner lining for blood vessels or other body conduits. More particularly, the present invention provides tubular structures which can be expanded in a transversal direction to conform to the diameter of a particular vessel in a patient""s anatomy.
B. Description of the Prior Art
Conventional vascular grafts have been used routinely for the repair of the human vasculature. These devices are typically flexible tubes of woven or knitted polyethylene terephthalate (PET or Dacron (copyright)), porous polytetrafluoroethylene (PTFE) or porous polyurethane (PU). Grafts of biological origin have also been used, typically comprising preserved human umbilical or bovine arteries. These conventional vascular grafts usually require invasive surgical procedures for insertion to expose at least the two ends of the segment of vessel to be repaired. Frequently, it is necessary to expose the entire length of the vessel segment. These types of procedures can cause major trauma to the patient with corresponding lengthy recovery periods, and may result in occasional mortality. In addition, grafts of various sizes are required to conform to the specific vasculature of a patient.
Other methods have evolved which use intraluminal vascular grafts, adjustable stents providing structural support, or a combination of both. These devices are preferably remotely introduced into a body cavity using a catheter type of delivery system. Alternatively, these devices may be directly implanted by invasive surgery. The intent of these methods is to maintain patency after an occluded vessel has been reopened using balloon angioplasty, laser angioplasty, atherectomy, roto-ablation, invasive surgery, or a combination of these treatments.
Intraluminal vascular grafts can also be used to repair and provide structural support to aneurysmal vessels, particularly aortic arteries, by inserting an intraluminal vascular graft within the aneurysmal vessel so that it can withstand the blood pressure forces responsible for creating the aneurysm. In this environment, intraluminal vascular grafts provide new blood contacting surfaces within the lumen of a diseased living vessel. Moreover, intraluminal grafts are not limited to blood vessels, but have other applications, such as the repair and reconstruction of urinary tracts, biliary ducts, respiratory tracts and the like.
In the prior art, an intraluminal graft is collapsed and inserted into a body conduit at a smaller diameter at a location remote from the intended repair site. A catheter type of delivery system is then used to move the intraluminal graft into the repair site and then expand its diameter to conform to the inner surface of the living vessel. Various attachments, including adjustable stents or barbs, may also be used to secure the intraluminal graft to the subject vessel at the desired location without the necessity of invasive surgery.
Various attempts have been made to provide intraluminal vascular grafts with or without stents. For example, an intraluminal vascular graft was suggested as early as 1912 in an article by Alexis Carrel (xe2x80x9cResults of the permanent intubation of the thoracic aortaxe2x80x9d, Surg., Gyn. and Ob. 1912;15:245-248).
Ersek (U.S. Pat. No. 3,657,744) describes a method of using one or more stents to secure a flexible fabric vascular graft intraluminally, the graft and stent having been introduced distally and delivered to the desired position with a separate delivery system. According to this patent, the graft is introduced to the patient at its final diameter, since the device is placed following surgical exposure and resection of the injury site. The stents are mechanically deployed by twisting an external apparatus.
Choudhury (U.S. Pat. No. 4,140,126) describes a similar method of repairing aortic aneurysms whereby a PET vascular graft is fitted at its ends with metal anchoring pins and pleated longitudinally to collapse the graft to a size small enough to allow for distal introduction. The barbed anchoring pins are deployed by advancing a wire to mechanically increase the diameter of the rings.
Rhodes (U.S. Pat. No. 5,122,154), describes endovascular bypass grafts for intraiuminal use which comprises a sleeve made of standard graft material and unidirectionally hinged stents. The graft is longitudinally pleated for introduction, and the stents are expanded in location by external means.
Lee (U.S. Pat. No. 5,123,917) describes an intraluminal vascular graft made of flexible, radially expandable material and balloon-expandable stents. The material and stents are both radially expanded in situ using, e.g., a balloon.
Gianturco (U.S. Pat. No. 5,507,771), describes a self-expanding stent assembly with an elastic covering for the prevention of restenosis. The entire device fully self-expands upon deployment.
Meyers (U.S. Pat. No. 5,700,285) describes a seamed, thin walled intraluminal PTFE graft with balloon expandable stents. A balloon is employed to expand the graft and stents in location.
Banas (U.S. Pat. No. 5,749,880) similarly describes a reinforced vascular graft with radially expandable PTFE coupled with balloon expandable stents. The graft and stents are stretched beyond their plastic limits by a balloon to deploy the device.
Fogarty (U.S. Pat. No. 5,824,037) describes modular tubular prostheses made of radially expandable cloth material and self-expanding stents. The graft material is expanded by balloon, and the stents provide radial support for the reoriented cloth fibers.
Martin (European Patent Application EP 0893108 A2,) describes a stent-graft with a ribbon affixing a portion of a stent to a PTFE graft.
All of these devices have a number of drawbacks that make them undesirable for clinical use. First, devices made of non-expandable materials and having predetermined deployed diameters cannot accommodate variations in patient physiology, and changes in diameter between the distal and proximal implantation site.
Second, devices with plastically deformable stents cannot withstand external compression without deformation of the stents, limiting the use of the devices in patient""s extremities.
Third, fully self-expanding devices must be deployed through a sheath, which typically compels the user to deploy the devices linearly, i.e. from the proximal to the distal end.
Therefore, it would be advantageous to provide an intraluminal device having a diameter which can be adjusted in vivo. It is further desirable to provide a device that is self-expandable so that it can recover from external compression. It is still further desirable to provide a device which can be deployed in a non-linear fashion, i.e., first attaching the proximal end, then attaching the distal end, and, finally adjusting the diameter of the device between the two ends.
It is an objective of the present invention to provide an intraluminal device which has initially a small diameter so that it can be introduced easily into the vessel of a patient from a remote location and which can be easily expanded in place to any desired diameter thereby conforming to the diameter of the vessel being repaired or reinforced.
A further objective is to provide an intraluminal device such as a stent graft including a conformable ePTFE tube and a self-expandable support stent.
A further objective is to provide a novel process for making a conformable ePTFE tube usable as an intraluminal device which can be radially deformed easily up to a preset diameter without exceeding its plastic deformation limit.
Other objectives and advantages of the invention shall become apparent from the following description of the invention.
An intraluminal device constructed in accordance with this invention includes at least one self-expanding stent affixed to a tube formed of a porous, conformable ePTFE. The term xe2x80x98conformable ePTFE tubexe2x80x99 shall be used herein to define a tube made from ePTFE using a particular process described below.
Porous ePTFE has a microstructure of nodes interconnected by fibrils, as taught in U. S. Pat. Nos. 3,953,566; 4,187,390 and 4,482,516. Typically, tubes of ePTFE have been made using a combined extrusion and longitudinal stretching process. A problem with these types of tubes is that because of the limitations of the machinery and processes used to produce them, their wall thickness becomes large once the tube diameters exceed 8 mm and hence cannot be used for many prostheses requiring grafts of up to 25 mm in diameter. Moreover, standard ePTFE tubes cannot be expanded radially because they have a tendency to lose strength and split when they are dilated.
A method of producing dilated ePTFE tubes with much larger diameters (up to 25 mm and more) with extremely thin walls (down to 0.008 inches and less) by progressive dilation of an initial ePTFE tube by an incremental amount followed by, calendering at a preselected temperature is taught by co-pending commonly assigned U. S. Pat. No. Application 09/244,343 by Colone et al. entitled xe2x80x9cMETHOD OF MAKING LARGE DIAMETER VASCULAR PROSTHESES AND A VASCULAR PROSTHESIS MADE BY SAID METHODxe2x80x9d filed Feb. 4, 1999, now U.S. Pat. No. 6,187,054, issued Feb. 13, 2001 and incorporated herein by reference.
In the present invention, an ePTFE tube which has been dilated by the process described above, is shrunk radially by inserting a small diameter mandrel into the dilated tube and heating the tube at a predetermined temperature. The present inventors have found that by heating the dilated ePTFE tube over a small mandrel causes the dilated ePTFE tube to shrink radially around the mandrel thereby producing a tube which is homogeneous and has an inner diameter determined by the diameter of the mandrel. The only limitation on this process is that the mandrel cannot have a smaller diameter than the inner diameter of the initial ePTFE (i.e., the tube made by extrusion). Importantly, the tube contracted in this manner can be readily expandable by applying radial forces to it. In fact the tube can be expanded radially up to its original dilated size without causing it to lose strength or split. In other words, the plastic deformation limit of this tube is essentially the diameter of the dilated tube. The tube produced by this process is called herein a conformable ePTFE tube to differentiate it from other ePTFE tubes suggested by the prior art.
A further advantage of a conformable ePTFE tube is that its different longitudinal sections can be radially expanded independently of each other. For example, the ends of a tube can be expanded first, followed by the middle section extending between the ends. Moreover, these different sections need not be expanded to the same diameter.
An intraluminal device produced in accordance with this invention comprises a conformable ePTFE tube which is preferably supported by a self-expandable stent. In this manner, the intraluminal device or stent-graft itself is self-expandable after being deployed and thus will recover to its expanded diameter if it experiences any outside compressive forces.
The term xe2x80x98self-expanding stentsxe2x80x99 refers to stents which, when released, increase in diameter automatically without the need for an external expansion means, such as a balloon or other similar means. Devices of this type include stents of braided wire, such as those taught by Wallsten U.S. Pat. No. 4,655,771, and stents of formed wire, such as those taught by Gianturco, U.S. Pat. No. 4,580,568. These stents expand to a large diameter after being released from a constraining force which restricts them to a smaller diameter. Self-expanding stents may be formed from nitinol wire as taught by PCT US 92/03481. These stents expand in diameter when exposed to a slight increase in temperature. The self-expanding stents employed in this invention are selected such that the radial force created when these stents are in their compressed state and inserted into a conformable ePTFE tube is less than the force needed to radially expand the conformable ePTFE tubes. The stents are further selected such that their maximum intended deployment diameter is less than their relaxed diameter, so that when deployed as intended (i.e. attached to a graft), they provide radial tension to the graft. In this manner, once the stents are affixed to a conformable ePTFE (as described more fully below), the tube is biased toward a cylindrical shape by the stent both before and after expansion.
The conformable ePTFE tubes and self-expanding stents may be adjoined when both devices are in their compressed state. Alternatively, a dilated PTFE tube and self-expanding stents may be adjoined first and then the ePTFE tube and the stents are contracted to a compressed size together. In either case, the production of said intraluminal devices is complete when the device is in its compressed state.
The conformable ePTFE tubes may be affixed to either the exterior surface or the luminal surface of the self-expanding stent. Alternatively, a first conformable ePTFE tube may be affixed to the exterior of the self-expanding stent and a second conformable ePTFE tube may be affixed to the luimnal position of the self-expanding stent. The first and second conformable ePTFE tubes may be affixed to each other in the spaces between or within the stents.
The conformable ePTFE tubes may also be affixed to the self-expanding stent with an adhesive. The adhesive may be a thermoplastic fluoropolymer adhesive such as fluorinated ethylene propylene (hereinafter FEP), perfluoroalkoxy (hereinafter PFA), polypropylene, or other similar material. The first and second PTFE tubes may then be affixed to each other by heating them above the crystalline melting point of the PTFE tubes adequately to cause the two coverings to thermally adhere, or alternatively they may be affixed by an adhesive such as FEP.
The stents may yet also be constrained between two tubes but be permanently affixed to neither. The two tubes are adhered to each other on their ends and in the spaces between and within the stents by thermal adhesion or fluoropolymer adhesive as described above.
The luminal device thus formed may be delivered percutaneously, typically through the vasculature, in its compressed state. Once reaching the intended delivery site, the tube (or tubes) and stents are radially and irreversibly expanded by a balloon or other means. In so doing, the self-expanding stents expand toward their relaxed diameter. However, as the stents do not reach their relaxed diameter, they remain in radial tension, biasing the tube against the vessel wall.